Radio age research, manufacturing, communications, broadcasting, television (1941)

Studies In Sound By Dr. Harry F. Olson RCA Laboratories, Princeton, N. J. EVERY MODERN FACILITY FOR RESEARCH INTO THE VAGARIES OF ACOUSTICS IS AVAILABLE AT RCA LABORATORIES public has enjoyed a continuous im- provement in the tone quality of radio receivers. Other important ap- plications benefited by this special- ized branch of research are phono- graphs, sound motion pictures, tel- evision, public address systems, world wide communications and many special wartime projects on huul and sea. Possibly the most interesting of all rooms in the group, in appear- ance and use, is the Free Field Sound Laboratory. The expression "free field", in this instance, means freedom from reflections, an essential condition in the testing of electro-acoustic trans- ducers, better known as micro- phones and loud speakers. And in the design of this Free Field Labo- ratory, RCA Laboratories' exi)erts have reached as close to perfection as the most sensitive instruments can determine. All Oddly Designed Room Acoustic engineers will tell you that the most obvious and direct solution of this problem of con- trolled reflections would be to make the measurements out of doors at a great distance from the earth and from any hill, house, or other re- flecting surface. But the elements, natural and man-made, are unpre- dictable noise makers and only by conducting the outdoor tests at great elevation could these objec- tions be overcome. For these rea- ROOMS with sound characteris- , tics that would both delight and dismay housewives and Swiss yodelers are only part of the scien- tific marvels that comprise the Acoustic Laboratory of the new RCA Laboratories at Princeton, N. J. One of the rooms is so devoid of echoes that the blood stream in a visitor's ears hisses ominously in the eerie silence of the place; a sec- ond is constructed in such a manner that a single burst of sound swells into a cacophony of noise. These unusual compartments, termed Free Field Sound Room and Reverberation Chamber respective- ly, together with a Sound Stage, a Magnetic Laboratory, a Living Room which can be adjusted to be- come either "dead" or "alive", and a Field Laboratory used for the outdoor testing of sound systems designed for operating in the air and under water, make it possible for RCA experts to carry out a wide range of precision tests on newly developed equipment. Acoustics, the science of sound behaviour, is the very heart of radio reproduction and as such plays a basic role wherever loud speakers and microphones are used. As a direct result of this unremit- ting search for better materials, methods and component parts, the sons a free field sound room be- comes an almost indispensable part of an acoustical laboratory. Designers of the room com- menced with one basic objective, viz., to reduce to a negligible amount all reflections from the boundary surfaces. This called for a room of considerable size with walls constructed of materials that would absorb instead of reflect sound waves. The combination of these two factors resulted in an acoustic measurement laboratory which immediately impresses the casual visitor as a creation straight out of the Walt Disney imagina- tion. Walls Heavily Baffled In constructing the room, en- gineers began with floor dimen- sions of 48 by 36 feet surrounded by walls 36 feet high. Inside these outer limits, one foot from walls, floor and ceiling, another structure was built of ozite one inch thick. Then a series of ozite strips, called baflles, eight feet in depth and spaced two feet apart were hung at right angles to the room sur- faces. And finally, sandwiched be- tween the baffles, the builders added still other baflles of the same mate- rial, four feet in depth. With these construction details completed, the laboratory measured 32 feet long, 20 feet wide and 20 feet high. A platform of steel grilhvork 12 by 24 feet, elevated 11 feet above floor level and supported on cushioned legs to absorb vibration, provides working space for personnel and test set-ups. How successful the acoustical en- gineers were in their execution of the room is best indicated by tests made after its completion. Meas- OVTDOOR TESTS OF SOUND EQUIPMENT ARE CONDUCTED AT THIS FIELD LABORATORY AT RCA LABORATORIES, PRINCETON, N. J. [12 RADIO AGE]